March 4 (Bloomberg) — After snubbing the 2012 Democratic National Convention, labor leaders are this year pledging a flood of cash and volunteers for the party's U.S. Senate candidates — and getting plenty in return.

Democratic leaders have shelved a measure to encourage free-trade agreements — which unions hate — and are moving to raise the minimum wage to $10.10 an hour. President Barack Obama is seeking more for labor-backed job training programs in his budget request. And workers are winning key decisions by the Democrat-dominated National Labor Relations Board, after Obama helped clear the way for it to operate again at full strength.

In return, Democrats will need all the help they can get as they seek to preserve a slender, 55-45 majority in the Senate. The November elections include competitive races in Michigan, Alaska, Montana and other states that have workforces with a higher-than-average percentage of union membership.